WO1999011404A1

WO1999011404A1 - Method and device for continuous or semi-continuous casting of metal

Info

Publication number: WO1999011404A1
Application number: PCT/SE1998/001563
Authority: WO
Inventors: Jan-Erik Eriksson; Magnus HALLEFÄLT
Original assignee: Abb Ab
Priority date: 1997-09-03
Filing date: 1998-09-02
Publication date: 1999-03-11
Also published as: SE9703170D0

Abstract

Method and device for continuous or semi-continuous casting of metal in a mould (10), in which a primary flow (P) of molten metal supplied to the mould through a port (21, 22) in a pouring nozzle (20) is acted on by static magnetic fields (30, 31, 32, 33) at a lower level (L) which is at or downstream of the nozzle port and at an upper level (U) which is between the top end of the mould and the nozzle port (21, 22). Magnetic circuits provided at both levels apply magnetic fields (30, 31, 32, 33) acting within two main zones (UA; UB; LA; LB) on opposite sides of the nozzle (20), and an intermediate zone (UI, LI), substantially subtending the width of the nozzle tube, is essentially free from magnets so that a substantially weaker magnetic flux density acts on the melt in the intermediate zone than in the main zones.

Description

Method and device for continuous or semi-continuous casting of metal

TECHNICAL FIELD

The present invention relates to casting of metals and more particularly to a method for continuous or semi-continuous casting of metal in which the flow of metal in a cast strand formed in a mould is acted on at an upstream level and a downstream level by static or low-frequency magnetic fields.

BACKGROUND ART

In continuous or semi-continuous casting of metals a metallic melt is poured into a mould and cooled therein to form a strand, which is continuously withdrawn from the mould. Depending on the cross-sectional dimensions of the open-ended mould chamber, the pro- duct obtained by cutting the strand to lengths is called billets, blooms or slabs. The primary flow of molten metal fed into the mould is at least partly solidified adjacent the walls of the mould chamber and at the point where the strand leaves the mould it comprises a mechanically self-supporting skin or shell surrounding a non-solidified centre.

Preferably, the mould is supported by beams, often called water beams, having internal cavities or channels for supply of a coolant to the mould. Typically, the mould comprises, at least in the case of a heavy-section square or rectangular strand, four plates made of copper or other material of suitable heat conductivity. The water beams typically are disposed around and in good thermal contact with the mould plates to fulfil their double function of supporting and cooling the mould.

During casting, the primary flow of molten metal is poured into the mould chamber either through an immersed nozzle, i.e. a nozzle dipping into in the melt (closed casting), or as a free tapping jet (open casting). These two alternative pouring methods create different flow situations and require different applications of the magnetic fields used to control the flow of molten metal in the mould. If the hot primary metal flow is allowed to enter the mould in an uncontrolled manner it will penetrate deeply into the cast strand. Such deep penetra- tion in the strand is likely to have a negative influence on the quality of the product and the productivity. Among other things, non-metallic particles and/or gas can be entrapped in the solidified strand. An uncontrolled flow of molten metal may also cause flaws in the internal structure of the cast strand. Moreover, a deep penetration by the flow of molten metal may cause local remelting of the solidified shell so that the melt penetrates the shell beneath the mould and causes severe disturbance and long downtime for repair.

To provide a solution to these problems and improved production conditions, European patent document EP-A1-0 040 383 proposes the application of one or more static magnetic fields to act on the incoming primary flow of molten metal in the mould in order to brake it and split it up and thereby control the flow pattern of the molten metal in the strand. A magnetic brake comprising one or more magnets applies the magnetic field. Advantageously, an electromagnetic brake, abbreviated EMBR, is used. EMBRs comprise one or more windings, such as multi-turn coils, around magnetic cores.

However, the flow of metal at the meniscus, i.e., the surface of the molten metal at the top of the mould, has also been found to be of decisive importance in respect of the quality of the cast product as described in European patent specification EP-B 1-0 401 504. According to this document, magnets are arranged to apply magnetic fields at two levels, an upper or upstream level and a lower or downstream level, by means of magnetic poles having a horizontal magnetic pole band area subtending essentially the whole width of the cast strand. The upper level is above and the lower level is below the outlet ports of the immersion nozzle.

According to EP-B 1-0 401 504 the magnetic fields are to be controlled such that there is sufficient heat transport to the meniscus to avoid freezing and also to establish conditions favourable to elimination of inclusions, mould powder and gas in the cast product. To this end, the flow velocity of the upwardly directed secondary flow and the flow at the meniscus has to be sufficiently high to avoid freezing, but at the same time the flow velocity at the meniscus must not be so high as to cause a risk that mould powder, oxides and gas bubbles are drawn down in the molten metal and entrapped in the cast metal. This control of the magnetic fields is effected by regulating the magnetic flux density using a mechanical control device to change the distance between opposed poles.

It has been found to be desirable, however, to further increase the flexibility in magnetic field distribution needed to ensure and maintain a good controlled flow in the mould throughout the casting, and also to allow one or more casting variables to be changed without thereby also changing the flow pattern in the mould such that production and/or quality variables are improperly affected.

Because the upper magnetic field in this case acts essentially across the entire width of the casting mould, it will also influence the flow within the immersed pouring nozzle used for the supply of the hot primary flow of molten metal into the mould. Such influence, however, is difficult to deal with, especially in respect of aluminium-killed steels or other steels containing oxide or other non-metallic particles, because the magnetic field will affect the flow within the nozzle and in particular influence the movements of particles.

In some cases, depending on the composition and size of particles, flow velocity etc., the result may be a deposition of particles on the internal nozzle surfaces and eventually clogging of the nozzle. The clogging will disturb the flow within the nozzle. To avoid clogging it is known to inject or purge argon or other inert gases in the nozzle or to use special tubular nozzles whose internal surfaces comprise a material that is not wetted by the particles, so that the surfaces will not be prone to attract deposition of particles. However, such measures are most likely to affect production costs or quality. Gas purging also tends to destabilise the flow normally developing in the upper part of the mould because it will create an upward flow of gas bubbles in the central part of the mould.

OBJECTS OF THE INVENTION

It is a primary object of the present invention to provide a method for continuous or semi- continuous casting of metal whereby a cast product with a minimum of defects is produced throughout the casting at the same or higher productivity, compared with prior art methods. Throughout the casting the method should bring about a lowering of the level of impurities and also improved capabilities to control the structure of the cast metal while maintaining or improving the casting speed, yield and other production parameters.

Because the flow at the meniscus has been found to be of decisive importance with respect to the exclusion of impurities, trapping of mould powder and gas, and the penetration of the hot primary flow has been found to be of decisive importance with respect to the capabilities to control the structure of the cast product and the mass and thermal transport in the mould, it is also an object of the present invention to improve the control of the flow at the meniscus and at the lower level downstream of the nozzle ports independently of each other throughout the casting by configuring the applied magnetic fields so as to ensure a minimum of trapping or accumulation of non-metallic inclusions, mould powder or gas in the cast products and to improve the capabilities to control the mass and thermal transport within the mould.

It is also an object of the present invention to provide a method whereby any magnetic fields acting on the melt within the tubular nozzle are minimised at a low level while maintaining a high magnetic field flux density in the areas around the nozzle both at the upper level to control the secondary flow at the meniscus, and at the lower level to brake and split the incoming primary flow. This will substantially reduce, if not eliminate, the magnetic fields affecting the flow within the nozzle tube and thus substantially reduce the risk of clogging the nozzle tube, thereby eliminating the need for a special tube material.

It is also an object of the present invention to provide a device for carrying out the method according to the invention.

Other objects, features and advantages of the present invention will became apparent from the a reading of the following detailed description of the invention and preferred embodiments thereof, including possibility to provide an improved and controlled flow pattern throughout the casting and the resulting improved capability to control the solidification conditions in the cast product and the conditions for excluding non-metallic impurities and avoiding entrapment of mould powder or gas in the cast products, so that the casting conditions can remain essentially stable throughout the casting. SUMMARY OF THE INVENTION

To achieve this, the invention provides a method for continuous or semi-continuous casting of metal according to the precharacterising portion of claim 1, namely a method in which a primary flow of hot molten metal supplied into a mould through at least one port in an immersed tubular nozzle is acted on by essentially static magnetic fields at a lower level, which is at or downstream of the nozzle port, and at an upper level, which is between the top end of the mould and the nozzle port, and in which the magnetic fields are applied by magnetic field generating means comprising magnets disposed adjacent to the mould along two opposite mould sides, characterised in that at each of the upper level and the lower level the magnetic fields are applied within two main zones on opposite sides of the nozzle, and in that the magnetic flux density in an intermediate zone substantially subtending the width of the nozzle is substantially lower than the flux intensity in the main zones.

In accordance with the invention there is also provided a device for carrying out the method according to the invention, which comprises:

- a mould for continuous or semi-continuous casting of metal, - a tubular immersion nozzle with one or more outlet ports adapted to be immersed in the melt in the mould during casting, and

- magnetic circuits comprising magnetic field generating means including magnets disposed adjacent to the mould along two opposite mould sides for applying essentially static magnetic fields to the melt at a lower level which is at or downstream of the nozzle port, and at an upper level which is between the top end of the mould and the nozzle port, characterised in that at each of the upper and lower levels the magnets are disposed essentially within two main zones on opposite sides of the nozzle, and in that an intermediate zone substantially subtending the width of the nozzle is essentially free from magnets so that the magnetic flux density in the intermediate zone is substantially lower than the magnetic flux density in the main zones. In a preferred embodiment of the method two oppositely directed magnetic fields are applied at each of the upper and lower levels and separated by the intermediate zone, whereby the melt in the mould is acted on by the magnetic fields substantially only within the two main zones.

The magnetic fields acting at one level may be applied by separate magnetic circuits but preferably a single magnetic circuit comprising pairs of magnetic poles applies them.

In an alternative embodiment the magnetic fields in the main zones at the same level have the same direction and preferably are applied by separate magnetic circuits.

In another alternative embodiment, each main zone has its associated magnetic poles subdivided such that the main zones are subdivided into sub-zones, each associated with a pair of magnetic sub-poles, preferably such that the direction of the magnetic field in any one sub-zone is opposite to the direction of the magnetic field in any adjacent sub-zone.

Preferred and alternative embodiments of the method and device according to the invention are characterised by features of the independent claims and will be described below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a view in vertical section showing a mould with magnetic fields configured according a first embodiment of the present invention;

Figure 2 is a view in vertical section along a plane through one of the main zones in Figure 1 and shows a mould with electromagnetic circuits arranged to apply the magnetic fields shown in Figure 1 ;

Figure 3 a view in horizontal section of the mould showing a preferred embodiment comprising a single magnetic circuit for providing the two magnetic fields acting in the main zones at each level; Figure 4 is a view in horizontal section of the mould at one of the upper and lower levels showing an alternative embodiment comprising two magnetic circuits at each level;

Figure 5 is a view in horizontal section of the mould at one of the upper and lower levels showing a further alternative where a plurality of paired magnetic poles are arranged to act within each main zone;

Figure 6 shows an electromagnet the iron core of which is divided into a plurality of sub- cores adjacent the mould; and

Figure 7 shows a magnetic pole with a pole plate inserted between the pole and the mould.

DESCRIPTION OF PREFERRED EMBODIMENTS, EXAMPLES.

As shown in Figure 1, a primary flow P of hot metal enters the mould 10 through side ports 21, 22 of an immersed tubular pouring nozzle 20. The metal is cooled in the mould and solidifies to form a strand which when leaving the mould comprises a self-supporting solidified skin or shell around a liquid centre region. The mould is supported by a support structure including beams (not shown in Figure 1) having internal channels for a coolant, such as water. The beams, often called water beams, supply a coolant to internal channels (also not shown in Figure 1) in the mould 10. As illustrated, the pouring nozzle 20 has two side ports 21,22 directed slightly downwardly toward the narrow sides 11, 12 of the mould, but this invention is applicable regardless of the configuration and number of ports and also when casting using an unshielded tap stream.

Magnets (not shown) are disposed to apply magnetic fields 30, 31 to act within the mould 10 at a first lower level L downstream of the nozzle ports 11,12. The magnetic fields 30,31 act essentially only within two main zones LA, LB on opposite sides of the nozzle 10. An intermediate zone LI subtending the width of the nozzle 10, is free from magnets, and the magnetic flux density of any magnetic field acting within this zone LI (such as border portions of the fields 30,31) is substantially reduced in relation to the magnetic flux density acting in the main zones LA, LB. The magnetic fields 30,31 at this lower or downstream level LA, LB brakes and splits the primary flow of molten metal and creates a controlled secondary flow s in the mould. Thereby the downward penetration of primary flow of molten metal into the solidified portion of the strand is reduced and the secondary flow s controls the mass and thermal transports within the mould.

To further improve this control, magnetic fields 32,33 are also applied at an upper or upstream level U within a region extending between the top end of the mould and the nozzle ports 21,22. For example, as shown in Figure 1, the magnetic fields 32,32 may be applied at or near the meniscus 15 formed by the molten metal in the mould. The magnetic fields 32,33 at this upper level U are also applied so as to act essentially only within two main zones UA,UB on opposite sides of the nozzle 20. As at the lower level L, the intermediate zone UI at the upper level U subtends the width of the nozzle 20 and is free from magnets so that the magnetic flux density of any magnetic field acting within this zone UI is sub- stantially lower than the magnetic flux density acting in the main zones UA, UB.

The magnetic fields 32,33 at the upper level main zones UA, UB provide a controlled secondary flow at the top end of the mould and, more importantly, at the meniscus 15. The controlled flow at the meniscus 15 ensures that non-metallic particles and gas are flotated and that mould powder is not drawn down into the liquid metal but forms a liquid film separating the cast strand from the mould. Thus, favourable thermal conditions and a controlled mass transport are created and maintained at the top end of the mould ensuring a clean metal with a low level of inclusions, low level of entrapped gas and high surface quality.

Preferably, and as shown in Figure 2, the magnetic fields 30,31,32,33 are applied by electromagnets comprising a core 41 and an electric coil or winding wound around the core 42. As likewise shown in Figure 2, the coils or windings 42 are disposed outside the water beams 50 which are mounted outside the mould 10 to support and cool the mould 10, while the cores 41 extend through the water beams 50 and face the mould 10. The water beams 50 and also the mould 10 comprise an integrated system of internal cavities 51,14 or channels for a coolant, preferably water, which is constantly supplied throughout the casting. Magnetic yokes 43 are arranged to form magnetic return paths closing the magnetic circuits.

In the preferred embodiment shown in Figure 3 a single magnetic circuit is provided at each level. This magnetic circuit comprises two pairs of magnetic poles disposed along the wide sides of the mould 10 to act essentially only within the main zones. As shown, the magnetic circuit comprises four magnetic cores 141, four windings 142, one around each core, and two yokes 143, each connecting or bridging the two cores 141 positioned on the same wide side of the mould. Consequently, the magnetic fields corresponding to the magnetic fields 30,31, 32,33 shown in Figure 1 , which are applied in the main zones on opposite sides of the nozzle 20 will thus be oppositely directed. Any portions of these fields extending into the intermediate zone accommodating the nozzle 20 will thus oppose and more or less cancel one another to make the intermediate zone essentially free from magnetic fields affecting the flow within the nozzle.

To further enhance the improved flow control, the windings 141 in the magnetic circuit acting at the upper level U and the windings 141 in the magnetic circuit acting at the lower level L are connected to separate power supplies so that they can be regulated independently of each other. In a preferred embodiment, the power supplied to the upper level L circuit is regulated on-line, on the basis of measurements of the secondary flow s in the mould 10.

As will be appreciated, each magnetic circuit may comprise two generally U-shaped cores, the ends of which face the mould on the same wide side of the mould, and a winding around at least one of the U-shaped cores.

In the alternative embodiment shown in Figure 4, two magnetic circuits are employed to create the same basic magnetic field configuration. Each of these circuits comprises two magnetic cores 241, two windings 242 and a single magnetic yoke 243 positioned at the narrow side 11, 12 of the mould 10 to bridge and connect the two cores aligned with one another across the associated main zone. A corresponding circuit can be formed from alternating core/yoke/winding assemblies, such as an integral core-yoke unit and one or more windings. Of course, this embodiment can also be used to apply two magnetic fields of the same direction acting in one main zone each as indicated in Figure 4.

In the embodiment shown in Figure 5, each of the main zones LA,LB,UA,UB is divided into a plurality of sub-zones a„a₂,a₃,a₄...a_n, b,,b₂,b₃,b₄...b_n. The magnetic fields applied in sub-zones of one and the same main zone may have a common direction, or their directions can alternate. The magnets applying the fields can be connected to a common power supply or they can be powered and controlled individually. For example, in the embodiment shown in Figure 5, each main zone may have four magnetic sub-zone fields a₁,a₂,a₃,a₄, b,,b₂, b₃, b₄ with the field directions changing from zone to zone. To this end, two magnetic circuits act in each main zone, each magnetic circuit comprising cores 341, windings 342 around the cores 341 and yokes 343.

At times, the casting variables are changed before a new casting operation is commenced and when the new casting variables are known, the configuration of the magnetic fields that is required for the new casting operation can be determined. To make it possible to configure the magnetic fields without changing the complete magnetic circuit, the present invention provides the magnetic arrangement shown in Figures 6 and 7.

The core 441 shown in Figure 6 comprises at its front end, i.e. the end positioned adjacent the mould, a plurality of sub-cores 441a, 441b, 441c, 44 Id, 44 le, 44 If. In the basic configuration all sub-cores comprise magnetic iron. To change the configuration, one or more of the sub-cores are removed and, if desired, replaced by an alternative sub-core of different magnetic permeability (sub-core 441c) or different dimensions (sub-core 44 le). An empty sub-core volume constitutes an essentially non-magnetic sub-core.

As an alternative to the divided front end of the core shown in Figure 6, magnetic inserts can be interposed between the core front end and the mould as shown in Figure 7. In Figure 7 a pole plate 70 comprising magnetic sections 71 and non-magnetic sections 72 is inserted between the core 541 and the mould 10. The method for continuous casting of a metal such as steel according to the present invention, e.g. as described in connection with any of the preferred embodiments, will produce a cast product, such as a continuos cast strand, with a minimum of defects. The low level of impurities, entrapped gas, casting defects, structural defects, surface defects etc. can be maintained throughout the casting while keeping the productivity at same or a higher level, compared with prior art methods.

In addition to advantages resulting from the improved capability to control individually the secondary flows at the meniscus and at the lower level downstream of the nozzle ports throughout the casting, the configuration of the magnetic fields according to the present invention offers the possibilities to customise the method in accordance with the conditions existing at each individual casting operation, and even to make adaptations to changing conditions during the casting. This has been found to be of decisive importance with respect to the capabilities to control the as-cast structure and the mass and thermal transport in the mould and to ensure and maintain elimination of impurities, avoid entrapment of particles or gas and prevent the primary flow from penetrating deep into the cast strand.

A further advantage resulting from the present invention is that magnetic fields acting on the melt within the immersion nozzle are minimised or eliminated, while a high magnetic field flux density is maintained in the areas outside the nozzle, both at the upper level to control the secondary flow at the meniscus and at the lower level to brake and split the incoming primary flow. This essentially eliminates the risks of magnetic fields affecting the flow within the nozzle and thus substantially reduces the risk of nozzle clogging, thereby eliminating the need for special nozzle materials and reducing the need for gas purging in the nozzle for the purpose of avoiding clogging.

A device for carrying out the method according to the invention is compact so that it lends itself to use with existing moulds where the space available for such a device is limited.

Still further advantages of the present invention include the capabilities to provide an improved and controlled flow pattern throughout the casting and thereby provide an increased capability to control the solidification conditions and the conditions for elimination of non- metallic impurities from the cast product and avoiding entrapment of mould powder or gas in the cast product, so that the casting conditions can remain essentially stable throughout the casting.

Claims

1. A method for continuous or semi-continuous casting of metal, in which a primary flow (P) of hot molten metal supplied into a mould (10) through at least one port (21,22) in an immersed tubular nozzle (20) is acted on by essentially static magnetic fields (30,31 , 32,33) at a lower level (L), which is at or downstream of the nozzle port, and at an upper level (U), which is between the top end of the mould and the nozzle port, and in which the magnetic fields are applied by magnetic field generating means comprising magnets disposed adjacent to the mould along two opposite mould sides, characterised in that at each of the upper level (U) and the lower level (L) the magnetic fields are applied within two main zones (UA,UB, LA,LB) on opposite sides of the nozzle, and in that the magnetic flux density in an intermediate zone (UI,LI) substantially subtending the width of the nozzle is substantially lower than the magnetic flux density in the main zones.

2. Method according to claim 1, characterised in that two oppositely directed magnetic fields are applied at each of said levels and separated by the intermediate zone (UI, LI), whereby the melt is acted on by the magnetic fields substantially only within the two main zones (UA JB, LA,LB).

3. Method according to claim 2, characterised in that the magnetic fields (30,31 ,

32,33) are applied by two magnetic circuits disposed at respective ones of the upper and lower levels (U,L), each magnetic circuit comprising a pair of magnetic poles for each main zone (UA,UB, LA,LB).

4. Method according to claim 3, characterised in that the magnetic fields are returned through a magnetic return path common to both magnetic circuits.

5. Method according to claim 1, characterised in that the magnetic field applied in each main zone (UA,UB,LA,LB) is divided into sub-zones (a₁,a₂,a₃,a₄...a_n,b₁,b₂,b₃,b₄...b_n) and in that the direction of the magnetic field in any one sub-zone is opposite to the direction of the magnetic field in any adjacent sub-zone.

6. Method according to any of the preceding claims, characterised in that the magnetic fields applied at the upper level (U) are controlled independently of the magnetic fields applied at the lower level (L).

7. Method according to claim 6, characterised in that each magnetic circuit comprises at least one electromagnet having an iron-cored electric coil and in that the electromagnets are powered from separate power sources.

8. Method according to any of the preceding claims, characterised in that the magnetic flux density at the upper level (U) is regulated on-line based on direct or indirect measurement of the flow velocity at the top end of the mould.

9. Device for carrying out the method according to any of the preceding claims com- prising;

- a mould (10) for continuous or semi-continuous casting of metal,

- a tubular immersion nozzle (20) with one or more outlet ports (21,22) adapted to be immersed in the melt in the mould during casting, and

- magnetic circuits comprising magnetic field generating means including magnets dispo- sed adjacent to the mould along two opposite mould sides for applying essentially static magnetic fields (30,31,32,33) to the melt at a lower level (L) which at or downstream of the nozzle port, and at an upper level (U) which is between the top end of the mould and the nozzle port, characterised in that at each of the upper and lower levels (U,L) the magnets are disposed essentially within two main zones (UA,UB,LA,LB) on opposite sides of the nozzle, and in that an intermediate zone (UI,LI) substantially subtending the width of the nozzle is essentially free from magnets so that a the magnetic flux density in the intermediate zone is substantially lower than the magnetic flux density in the main zones.

10. Device according to claim 9, characterised in that the magnets comprise magnetic poles acting in pairs, the poles of each pair being of opposite polarities and associated with the same main zone (UA,UB, LA,LB) on opposite sides of the mould.

11. Device according to claim 10, characterised in that two of said pairs of magnetic poles are disposed side by side on each of two opposite sides of the mould at least at one of the upper and lower levels (U,L) and associated with respective ones of the main zones (UA,UB, LA.LB).

12. Device according to claim 11, characterised by a first magnetic circuit at the lower level (L) and a second magnetic circuit at the upper level (U), each circuit comprising two pairs of magnetic poles, one pair being associated with each main zone (UA,UB, LA,LB).

13. Device according to claim 10, characterised in that the main zones are divided into a plurality of sub-zones and in that a plurality of paired magnetic poles are disposed along the width of the mould, each pair acting within one of the sub-zones (aΓÇ₧a₂,a₃,a₄...a_, bΓÇ₧b₂, b₃, b₄...b_n).

14. Device according to claim 13, characterised in that the magnetic poles acting in adjacent sub-zones (aΓÇ₧a₂,a₃,a₄...a_n, b,,b₂,b₃,b₄...b_n) are of opposite polarities.

15. Device according to any of claims 9 to 14, characterised by means for controlling the magnetic fields at the upper level (U) independently of the magnetic fields at the lower zone (L).

16. Device according to claim 15, characterised by a sensor for direct or indirect measurement of the flow velocity at the top end of the mould associated with means for regulating the magnetic flux density of at least one of the magnetic fields (30,31,32,33) online based on flow measurement.

17. Device according to any of claims 9 to 16, characterised by magnetic circuits comprising at least one iron-cored electric coil powered from an electric power source.

18. Device according to claims 12 and 17, characterised in that the first and second magnetic circuits are powered from separate power sources.

19. Device according to claim 17 or 18, characterised in that the cores comprise one 5 or more sub-cores (441 a,441 b,441 c,441 d,441 e,441 f) adj acent to the mould and in that the axis of each sub-core is oriented in the direction of the magnetic field passing through the core.

20. Device according to claim 19, characterised in that at least one sub-core (441a, 10 441 b, 441 c, 441 d, 441 e, 441 f) is movable in said direction.

21. Device according to any of claims 19 or 20, characterised in at least one sub-core (441a,441b,441c,441d,441e,441f) is made from a magnetic material and one or more other sub-cores are made from a non-magnetic material.

15

22. Device according to any of claims 9 to 21, characterised by a plate (70) comprising a magnetic material (71) which is interposed between the mould and the poles.

23. The use of the device according to any one of claims 9 to 22 for continuous of

20 semi-continuous casting of a metal or alloy, particularly aluminium-killed steel, containing non-metallic particles